Production methods of conventional polyurethanes depend on toxic isocyanates, which, in turn, are produced from even more hazardous phosgene. In recent decades, new methods of synthesis of nonisocyanate polyurethanes were developed. Today, polyhydroxyurethane networks based on petroleum-derived nonisocyanate materials are well known. For example, U.S. Pat. No. 5,175,231 issued in 1992 to Rappoport, et al, describes hydroxyurethane that is formed by a new method that does not require the use of isocyanate. The urethane is formed by reacting a compound containing a plurality of cyclocarbonate groups with diamine in which two amine groups have different reactions with cyclocarbonate so as to form a urethane oligomer with terminal amine groups. The compound with cyclocarbonate groups is the product of a reaction of a multifunctional polyetherepoxy with carbon dioxide in the presence of a catalyst, the conversion of epoxy groups into cyclocarbonate groups being 90 to 97 percent. The urethane oligomer can then react with epoxy resin to form cross-linked polyurethane.
U.S. Pat. No. 6,120,905 issued in 2000 to Figovsky describes certain polyhydroxyurethane networks that are produced based on reactions between oligomers comprising terminal cyclocarbonate groups and oligomers comprising terminal primary amine groups. Oligomers comprising terminal cyclocarbonate groups are the products of epoxy resins reacting with carbon dioxide in the presence of a catalyst, the conversion of epoxy groups into cyclocarbonate groups being 85 to 95 percent. U.S. Patent Application Publication No. 20100144966 published in 2010 to Birukov, et al, proposes a liquid cross-linkable oligomer composition that contains a hydroxyurethane-amine adduct and a liquid-reacting oligomer. The hydroxyurethane-amine adduct is a product of an epoxy-amine adduct reacting with a compound having one or more terminal cyclocarbonate groups. U.S. Pat. No. 7,232,877 issued in 2007 to Figovsky, et al, describes a method and an apparatus for synthesis of oligomeric cyclocarbonates from epoxy compounds and carbon dioxide in the presence of a catalyst. Unfortunately, all of these methods rely on the use of commercial petrochemical starting materials.
A detailed review of polyhydroxyurethane networks and methods of preparation was presented by Figovsky and Shapovalov in “Cyclocarbonate-based Polymers Including Non-Isocyanate Polyurethane Adhesives and Coatings” in Encyclopedia of Surface and Colloid Science, Somasundaran. P. (Ed), V. 3, 1633 to 1653, New York, Taylor & Francis, 2006.
Potential worldwide demand for replacing petroleum-derived materials with renewable plant-based materials is quite significant from the social and environmental viewpoints. Native oils and fats are the most important renewable raw materials for use in the chemical industry. During the last few years, modern synthetic methods have been applied extensively to fatty compounds for selective functionalization of the alkyl chain and have provided a large number of new fatty compounds from which interesting properties are expected (refer to Biermann U., Friedt W., Lang S., Lühs W., Machmüller G., Metzger J. O., Klaas M. R. G., Schäfer H. J., and Schneider M. P, “New Syntheses with Oils and Fats as Renewable Raw Materials for the Chemical Industry” in Angewandte Chemie International Edition, 2000, Volume 39, (13), 2206 to 2224).
Composites based on epoxidized unsaturated fatty acid triglycerides, transformed by various methods, and cured at elevated temperatures are disclosed in U.S. Pat. No. 6,121,398 issued in 2000 to Wool, et al. Among the various derivatives of epoxidized triglyceride oils, products of reactions with carbon dioxide (CO2) deserve special attention (Tamami B., Sohn S., and Wilkes G. L., “Incorporation of Carbon Dioxide into Soybean Oil and Subsequent Preparation and Studies of Nonisocyanate Polyurethane Networks” in Journal of Applied Polymer Science, 2004, 92 (2), 883 to 891).
Wilkes, et al, describe a method of carbonation of vegetable oils and preparation of polyhydroxyurethane networks in U.S. Pat. No. 7,045,577 issued in 2006. Reaction of carbonation of epoxidized soybean oil (ESBO) was conducted at ˜110° C. and atmospheric pressure in the presence of a catalyst (tetrabutylammonium bromide, TBABr) for approximately 70 h. Conversion of oxyrane (epoxy) groups to 2-oxo-1,3-dioxolane groups (cyclic carbonate groups) in carbonated soybean oil (CSBO) was 94%. To prepare polyhydroxyurethane networks, CSBO was mixed with different amines and heated at 70° C. for 10 h and then at 100° C. for 3 h whereby a non-durable flexible polymeric material (tensile strength σt=0.2-1.5 MPa; elongation at break ε=70 to 170%) was obtained.
Synthesis of CSBO from ESBO and CO2 at temperatures of 80 to 120° C. and pressure from atmospheric to 10.6 MPa in the presence of catalysts is described by authors K. M. Doll and S. Z. Erhan of the National Center for Agricultural Utilization Research, U.S. Department of Agriculture, Agricultural Research Service (IL). The improved synthesis of carbonated soybean oil using supercritical carbon dioxide at a reduced reaction time is addressed in Green Chemistry, 2005, 7 (12), 849 to 854 by Doll K. M. and Erhan S. Z., “Synthesis of Carbonated Fatty Methyl Esters Using Supercritical Carbon Dioxide” and in Journal of Agricultural and Food Chemistry, 2005, 53 (24), 9608-9614; and also by Holser R. A. in “Carbonation of epoxy methyl soyate at atmospheric pressure” in Journal of Oleo Science, 2007, 56 (12), 629 to 632.
An epoxy resin modified with CSBO was studied when cured with a polyamine hardener at room temperature (Parzuchowski P. G., Jurczyk-Kowalska M., Ryszkowska J., Rokicki G., “Epoxy Resin Modified with Soybean Oil Containing Cyclic Carbonate Groups” in Journal of Applied Polymer Science, 2006, Vol. 102, No. 3, 2904 to 2914). Reaction of carbonation of ESBO was conducted at 130° C. at a pressure of 6 MPa in the presence of a catalyst for approximately 120 hr. Conversion of epoxy groups to cyclic carbonate groups in CSBO was 98.3%.
Each polymer network sample consisted of a commercial epoxy resin, CSBO, and a polyamine-curing agent with two primary amino groups. All formulations were mixed with a stoichiometric amount of amine hardener. The curing process consisted of two methods. In the one-step method, epoxy resin was mixed with CSBO, and then the amine was added and cured at room temperature for 12 h. In the two-step method, carbonated oil was caused to react with the amine hardener at 70° C. for 3 h, and then the resulting viscous adduct was mixed with epoxy resin and cured under the same conditions. The samples contained from 5 to 40% of CSBO and had the following properties: tensile strength σt=40-70 MPa; elongation at break ε=6-10%. The products in the one-step method demonstrated higher mechanical properties in comparison with the two-step method.
Polyurethanes obtained by means of a nonisocyanate route were prepared by reacting CSBO with different diamines (Javni I., Hong D. P., and Petrović Z. S., in “Soy-based polyurethanes by nonisocyanate route” in Journal of Applied Polymer Science, 2008, 108 (6), 3867 to 3875). Studied was the effect of amine structure and carbonate to amine ratio on polyurethane structure and mechanical, physical, and swelling properties. The reactants, such as 1,2-ethylenediamine, 1,4-butylenediamine, and 1,6-hexamethylenediamine were used with a carbonate-to-amine ratio of the following: 1:0.5, 1:1, and 1:2. Samples were cured at 70° C. for 10 h and then for 3 h at 100° C. Along with urethane formation, the amine group reacted with ester groups to form amides. All amines produced elastomeric polyurethanes with glass transitions between 0 and 40° C. and hardness between 40 and 90 Shore A. At a stoichiometric carbonate-to-amine ratio, mechanical properties were the following: tensile strength σt=4.0-6.0 MPa and elongation at break ε=90 to 190%. The reaction of ESBO with carbon dioxide was optimized (temperature 140° C., pressure 10.3 MPa, catalyst TBABr, and duration 25 h) resulting in complete conversion of epoxy to cyclic carbonate groups resulting in polyurethanes with higher cross-linking density and much higher tensile strength than previously reported for similar polyurethanes. Swelling in toluene and water depended on cross-linking density and polarity of polyurethane networks controlled by the cyclic carbonate-to-amine ratio.
Kang, et al (Chinese Patent No. 1880360A, issued in 2006) describe catalytic carbonation of ESBO to 42 to 88% conversion and subsequent generation of nonisocyanate polyurethane (NIPU) using the following procedure: mixing with amine at 70 to 80° C. after synthesis of CSBO, densifying at 100 to 110° C. for 7 to 8 h, solidifying at 90° C. for 24 h, and placing at room temperature for 7 to 9 d. The cured NIPU had a tensile strength of σt=3.1-6.9 MPa and elongation at break ε=144 to 206%.
Chinese Patent No. 101260232A issued to Kang, et al, in 2008 relates to a mixed type of NIPU. The composition that contained CSBO, epoxy resin (10 to 50%), amine and catalyst was cured. The curing procedure corresponded to the one used in the aforesaid Chinese Patent No. 1880360A; cured samples had tensile strength and elongation at break from 1.5 MPa and 146% (for 10% addition of epoxy resin) to 49 MPa and less than 1% (for 50% addition of epoxy resin).
In the work by Li Z., Zhao Y., Yan S., Wang X., Kang M., Wang J., and Xiang H. in “Catalytic Synthesis of Carbonated Soybean Oil”, Catalysis Letters, 2008, 123 (3,4), 246 to 251), CSBO was used as an intermediate for the synthesis of NIPUs. CSBO was prepared by the reaction of ESBO with CO2 using a new composite catalyst comprising SnCl4.5H2O and TBABr. Results showed an obvious improvement in ESBO conversion using the present composite catalyst under mild conditions. Moreover, it should be noted that very high purity of CSBO was not a prerequisite for synthesis of NIPUs with good performance.